Gas saving mode at 25mph

I read up on it. I stand corrected that the injectors are turned off for brief periods of time. However, combustion continues with what fuel remains, and if it decreases too far to where there would be too much air going into the catalytic converters it will pulse the injectors to maintain combustion. The truck doesn't ever deactivate cylinders, and combustion never ceases.

Enough of the thread jacking, for the OP, here's a link. It is a little older, but the engine is the same, and Mike Sweers talks about the knock on deceleration. It has absolutely nothing to do with fuel being shut off.
https://www.autonews.com/article/20...-engineer-defends-choice-of-carryover-engines

 

Even my old 3uzfe has fuel cut. 2uzfe also has it I believe.

No clunking though. My moms GX460 is the clunkiest drivetrain I’ve ever had the pleasure of driving. She’s had two GX460’s and both did it so I always just assumed it was because of the full time 4WD.

 

Yeah, the GX is notorious for the rear driveshaft slip yoke clunk. Make sure it gets greased every service. (Some places don’t ever grease it)

 

I don’t hate a lot of things but keeping a leaking grease gun around is one of them. All the ones I’ve ever bought leaked before I could even get through half the tube of grease.

 

it happens when I accelerate, is very reproduceable, happens every time. Not sure if fuel shutoff has anything to do with it. It is late now but tomorrow I will try using S mode while the 'choke' is still on (so fuel does not shut off) and seeing if I coast in reduced gear at 30 mph and accelerate if I get the same noise. Will point to slack in the drivetrain if still does it.

 

you are not old just following the speed limit. lol
You can even get a ticket doing 29 in 25

 

I have actually felt this numerous times myself in the first 800 miles truck has now. Only at low speed like you’re saying. Scared the hell out of me the first couple times lol. I’ve been trying to figure out how to replicate it so I could show dealer. Searched on here and couldn’t find anything so figured it must not be a common tundra thing.

 

thank sweet baby Jesus it doesn't. That shit is nothing more than a gimmick

 

Yep, I don't know about the automatics, but the manuals would cut fuel above a specific RPM when the throttle was closed.

 

I was under the impression the torque converter was pushing things at that point but I'm not sure where I got that idea or how exactly it's supposed to work.

 

I believe that is correct, but combustion is still occurring.

 

How is combustion happening without fuel?

 

Gear backlash combined with axle rotation and motor mount deflection. When the pcm cuts fuel the torque is applied to the axle/driveshaft/transmission in the opposite direction and the whole system moves a bit.

If the driveshaft slip joint is a tiny bit stuck that will make the clunk bigger

 

If you watch in live time the dfco on the Tundra is very inconsistent. If you touch the throttle for just a second it will cancel it most of the time and it usually won't cut fuel when canceling cruise unless the brake pedal is pushed.

If you want to be sure for it to dfco, be >35mph with foot depresssing the accelerator pedal at least 5 seconds and release. Do not touch again

I wish it was like my old Honda: over 25 mph and in gear and foot off the pedal = always dfco, no other variables

 

How is there still the same exhaust and engine sound without combustion? Also, read the info that Viktor posted a pic of in the last post on page 1. The whole thing. It pulses the injectors if the air content would get high enough to cause issues at the cats.

My best guess is that the fuel pulse happens frequently enough to maintain combustion. Think about how rapidly and often combustion happens in an engine. It could cut fuel repeatedly throughout the process in small amounts to decrease fuel usage, and still pulse it often enough that our human senses couldn't detect it. It would sound like continuous combustion.

Kinda like the LED DRLs. Look at it with your naked eye and its constant, but point your phones camera at it and the pulses appear. How does it shine light when it clearly turns off? Same thing here for fuel cut off?

 

That is what I am trying to figure out as well. Does this happen on all trucks or just some.

I tested today in s3,s4,s5 modes while engine was still cold. Got to 30 let it coast to 25 then applied the throttle. No slack or clunking at all.

I will need to take it to Toyota service and see what they say.

 

( My wife tells me to just drive faster and problem solved.)

WaLaa...
Your Wife’s got some wisdom.
.

Welcome aboard from NorCal.

 

It's not combustion you're hearing. If you really want to find out, decelerate in a low gear down a hill or something and kill the engine. The sound doesn't change. I don't recommend it because you lose power brakes and power steering, but maybe then you'd be able to wrap your head around it.

From a technical standpoint you don't want any sort of meaningful combustion taking place under deceleration. Cylinder compression is too low and manifold vacuum is too high which is a recipe for unspent fuels and misfires. I'm aware that the injectors will pulse if needed, but it's not a constant cycle, if at all in most real world cases. I use engine braking when coming down mountain passes, and I can tell when they kick on because you can feel the speed pick up, then slow down again. I think it opens the throttle blade a little to let some air in. Maybe @ViktorG can enlighten me a little on that.

 

Op,

Fyi
I tried what you did and didn't hear any noise. Mine is a '16.
Going to read your post again and try again ...

 

Oh. Your inception game is strong sir. I salute you.

 

Thats basically a fancy vacuum guage.
Less pedal = more vacuum = better economy
More pedal =less vacuum = more fuel used.

It really is that simple.

 

Some?

 

And you can see this in realtime with an afr gauge. Use engine braking and afr goes max lean.

 

what speed does engine braking turn off at on the 2016? I know my 2015 would engine brake at 45 mph but never figured out at what speed it turns off. On my 2020 it turns off at 22mph.

To figure out what speed it turns off at bring it to 45 and release the throttle. Engine pitch will change (rpms increase slightly) as the torque converter locks and fuel is shut off. Will feel the truck slowly but very slightly.
At some speed the engine braking will turn off. Torque converter will unlock (rpms will drop slightly), gas will be injected again and truck will cost easer.

 

My '00 tundra would clunk when the driveshaft needed grease too. the 2020 doesn't do that yet, but that's the first thing I'd check when/if it does.

 

That indicator isn’t exact. It kind of represents your mpg, but it takes a second to register and reflect changes, so that’s why it shows 0 when you take your foot off the gas pedal, then gives a reading again a second or so later (which happens to coincide with the 20mph in your example).

You can reassure yourself this is true by doing the opposite: cruise along at any old man speed you like then, when you check your mirrors and see @hagrid coming up behind you, punch and hold the gas pedal. The truck will do what V8’s do, but that mpg indicator will lag a bit in showing you a fully-pegged (ALL the gas) mpg reading.

Try it. It’s fun!

 

My other car is a 2002 Honda Civic si(manual transmission). When I take my foot off the gas and coast to a stop it makes some beautiful sounds that can be heard indoors in houses I am passing by. But those sounds only happen when no fuel is being injected. Once it slows down enough where the gas starts flowing again the beautiful noise goes away.

 

Coasting

 

What kind of old man goes 5 over the limit!!!!!

 

Is that also called the propeller shaft? I believe that's what they call it in the manual?